These floating fortresses appear in all missions (Excluding boss missions) and spawn Ranx.
Round, red, and floating, these fortresses are big, non moving, and unattackable. They have green lights flashing on each spawner turret.
Attempting to attack directly when in the air is useless, Shirikens and darts don't do anything. Instead, attack them when all Ranx are killed, and slice them to bits. Most summon force fields when Ninja approaches them.